MEMS is a micro electromechanical system which integrates a micro sensor, an executer and a signal processing and controlling circuit, an interface circuit, communication and a power supply as a whole. In recent years, the traditional mechanical quantity sensor is progressively replaced by the MEMS pressure sensor in the fields of automotive electronics, consumer electronics and industry electronics, and has broad market prospects. For example, each of a tire pressure monitoring pressure sensor, an engine oil pressure sensor, an automotive braking system air pressure sensor and an automotive engine intake manifold pressure sensor widely adopts the MEMS technology.
As compared to the traditional mechanical sensor, the MEMS pressure sensor has a smaller size, a higher control precision and a manufacturing technical compatible with the silicon integrated circuit (IC) technology. Therefore, the performance/cost ratio of the MEMS pressure sensor is greatly improved. At present, the MEMS pressure sensor includes a piezoresistance type pressure sensor and a capacitive type pressure sensor, either of them is a MEMS sensor manufactured on a silicon chip.
The capacitive pressure sensor has a film plate capacitor structure which takes the air as the isolation dielectric. When a film electrode of the plate capacitor is deformed by external pressure and thus its capacitance is changed, a capacitance value is converted to a voltage signal via a signal processing circuit, and then the voltage signal is amplified and output. Therefore, the capacitive pressure sensor has a higher measuring precision and lower power consumption.
In the prior art, the capacitive pressure sensor is manufactured through the method of polycrystalline silicon deposition and oxide layer etching. An polycrystalline silicon film after being released is taken as a sensitive diaphragm in this method. The sensitive diaphragm is deformed under an external pressure to cause a change of the capacitance.
However the problem is that, in the manufacturing method of the above traditional capacitive pressure sensor, a pressure sensor chip and a signal processing circuit chip are discrete chips, and integrated by a packaging process after respectively manufactured. Either of a plastic packaging with a cavity and a cover, or a metal-can packaging has a complicated packaging process, and is not easily compatible with a mature IC manufacturing technology. Further more, the sensor has a larger size and a higher cost.
In addition, the sensitive diaphragm of the traditional capacitive pressure sensor is usually on the uppermost surface of a chip, and is vulnerable to be damaged in case of silicon substrate thinning and the chip packaging, thus the production yield is impacted. Furthermore, the pressure sensor chip and the signal processing circuit chip need to be respectively covered by protective gel to protect them from external environmental influence, resulting in higher cost of the capacitive pressure sensor.